This invention relates to a laser of the kind having a three-surface retroreflector.
The invention relates particularly to methods and apparatus for producing preferential polarization of the output light beam from a laser of the kind having a three-surface retroreflector.
When the output beam of a laser is used for cutting, the output light beam needs to be linearly polarized. This is an application's requirement. Linearly polarized light comes out at 45 degrees and is put through a quarter wave plate which makes circularly polarized light so that the light beam can cut steel or metal in both the X and Y directions with equal efficiency.
If the output light beam is randomly polarized, the light beam will produce different cut qualities when cutting contours.
By circularly polarizing the light, the same cutting efficiency is obtained no matter what direction the contour is being cut.
To get circularly polarized light, linearly polarized light is used as a starting point and is put through a special optic. So the laser needs to have linearly polarized light coming out of it.
One way of producing linearly polarized light at the output of a laser is to use a fold mirror mounted at 45 degrees within the path of the light beam resonating in the laser cavity. This produces polarization because the S and P reflectivities are enough different to cause the light to go into one mode, which is the highest efficiency, the least losses. In this polarization mode the polarization vector is in the plane of the maximum reflection of the S and P reflectivities.
Using an extra mirror in association with the laser cavity in this way requires extra structure and involves greater optical complexity because of the addition of the extra mirror.